Kaisei Arakawa is a young rakugoka, a traditional Japanese storyteller, affiliated with the Arakawa School. He holds the rank of futatsume, a mid-level professional status that he achieved at the notable age of nineteen, accomplishing this promotion within just two years of beginning his apprenticeship. He is the first disciple taken in by his master, Issho Arakawa, and is considered one of the most promising and talented performers of his generation.

Kaisei's background is marked by a formative childhood experience. He often visited the bar run by his mother, where a frequent customer was Issho Arakawa. When Kaisei’s mother later fell ill, Issho generously paid for her medical expenses. Touched by this kindness and curious about the profession that afforded it, a young Kaisei learned that Issho was a rakugoka. This act of generosity and the inspiration he drew from it became the driving force behind his decision to pursue the art, leading him to join the Arakawa School.

In terms of personality, Kaisei is a complex figure who presents a carefully managed exterior. On the surface, he is ambitious, talented, and proud, with a flamboyant and playful demeanor. He can be overly familiar, with a clingy nature that sometimes disregards personal space, yet he is also capable of deep loyalty and gratitude, particularly towards his master, Issho. He enjoys making people laugh and is known for his strong sense of humor in his performances. Beneath this cheerful and kind exterior, however, Kaisei harbors a darker, more ruthless ambition. He is intensely competitive and views other highly talented individuals as obstacles, even expressing a desire to eliminate them, a truth that his happy-go-lucky personality effectively masks.

Kaisei’s most notable ability is his distinctive rakugo style, which has been described as the art of seduction. Despite possessing a naturally deep voice, he is remarkably skilled at portraying female characters with realistic and captivating voices. His performances often feature sensual and comedic characters, and he has a particular talent for shifting the mood, using a silly facial expression to suddenly break a sensual atmosphere and turn it into something comedic. This technical mastery and his calm, disciplined approach on stage make him a formidable presence in the rakugo world.

Within the story, Kaisei serves as a significant rival and a key figure who recognizes the potential of the protagonist, Akane Osaki. During their first meeting, he is impressed by her abilities and recommends that she become a student of his own master, Issho Arakawa. He is thus a direct senior figure in the same school, often acting as an obstacle whose high level of skill forces Akane and other characters to refine their own art. His key relationships are central to his role: he is fiercely loyal to his mentor, Issho Arakawa, and is determined to follow in his master's footsteps. He also has a connection to Koguma Arakawa, another apprentice of Issho, whose advice becomes important to Akane when she faces Kaisei in competition.

Kaisei's development is defined by his rapid rise and the duality of his nature. His promotion to futatsume at nineteen, the only promotion Issho has granted in six years, marks him as a prodigy. His journey is shaped by his gratitude towards Issho, yet his own ruthless ambition to be the best suggests a potential future conflict between his public persona and his private drive. He is presented as a leader of the new generation in rakugo, but one whose path to the top is paved with a cold willingness to dismantle anyone he deems a threat.